Influences of temperature, salinity and irradiance on growth of Prorocentrum minimum (Dinophyceae) from the Mediterranean Sea

A Mediterranean clone of the red-tide forming dinoflagellate Prorocentrum minimum was studied in vitro for its capacities to adapt to salinity, temperature and light. This clone is euryhaline and shows optimal growth between 15 and 35‰. After adaptation, slow growth was observed at salinities as low as 5‰. An apparatus generating crossed gradients of temperature and light allowed 100 combined experimental conditions to be studied. Variations in lighting between 30 and 500 (μmol photons m−2 s−1 had little effect on growth, and no photoinhibition occurred. The clone can grow between 8 and 31°C, but is thermophilic with an optimal growth between 18 and 26.5°C. As a result of large variations in temperature from 18°C down to 10°C and maintained at 10°C, small spherical structures (8–10 μjn) were observed; they are described as temporary cysts. These results were compared to those obtained by different authors, in vitro and in situ, notably in the Mediterranean region.